We can finally know the origin of a mysterious stream of the Milky Way


As Joramangandra encircles the Earth, so does the entire galaxy. A massive, high-velocity stream of gas is wrapped around the Milky Way at a distance of about 200,000 light-years.

We know where it comes from, more or less. It is very clearly associated with large and small magellanic clouds, dwarf galaxies that orbit and eventually will be cannibalized by the Milky Way. It gives the Cosmic Snake its name – Magellanic Stream.

However, although the Magellanic stream chemically coincides with the Magellanic clouds, there is one aspect that has surprised astronomers for decades – its mass. There are about one billion solar mass gases in that stream, and models could not explain why the two satellite galaxies were losing so much.

“That’s why,” explained astronomer Elena D’Oghia of the University of Wisconsin-Madison, “We have come up with a new solution that is excellent at explaining the mass of the stream.”

According to their new model, the gas itself does not come from within the Magellanic clouds. Rather, it is derived from their galactic aura – massive clouds of gas and plasma that cover most galaxies.

All sky views of Magellanic Stream. (D. Nidevar et al., NRAO / AUI / NSF, A. Mellinger, Leyden-Argentina-Bonn Survey, Parks Observatory, Westerbork Observatory, RCBo Observatory)

The dance of the Magellanic Clouds and the Milky Way is an interesting one, in which the two satellite galaxies orbit each other, and then orbit the larger Milky Way simultaneously. This complex interplay is affecting all three galaxies, and the Milky Way is believed to disrupt the Magellanic Clouds.

Previously, it was thought that tidal disintegration from the Milky Way ejected the Magellanic Stream as two dwarf galaxies came under the Milky Way’s field of gravity effect. But this model can only take about 10 percent of the observed mass of the stream.

“The stream is a 50-year puzzle,” said astronomer Andrew Fox of the Space Telescope Science Institute. “We’ve never had a good explanation of where it came from. What’s really exciting is that we’re closing in on the explanation now.”

What is new here recently suggests that the Magellanic clouds are largely their own aura.

The team, led by astronomer Scott Luschini of the University of Wisconsin-Madison, conducted its own simulation of the magellanic clouds being orbited around the Milky Way.

He calculated that the halo of hot gas around the Magellanic Clouds – termed the Magellanic Corona – would dramatically change the way the Magellanic Stream formed.

According to their simulations, formation was a two-stage process. The first phase occurred long before the Magellanic Clouds were captured by the Milky Way, but while they were still orbiting each other. The larger Magellanic cloud stole a whole bunch of material from the smaller Magellanic cloud, destroying small amounts of gas on its own.

The process took about 5.7 billion years, occurring in a halo of gas with a mass of about 3 billion solar masses, which had captured two galaxies by the Milky Way. At this point, gravitational forces sow the seeds for the Magellanic Stream, with the halo providing about 10 to 20 percent of its final mass.

Animation MCSimulation Animation. (Elena D’Onghia and Scott Luschini / University of Wisconsin-Madison)

In the second phase, after the two galaxies are captured in the orbit of the Milky Way, our galaxy’s gravity and interaction with the galactic halo itself creates approximately one fifth of the mass of the rest of the Magellanic corona, creating the remaining current.

According to the team’s simulations, this two-stage sequence of events reproduces the structure and mass of the Magellanic Stream, including the branch of the stream called the pioneer branch that orbits around the two dwarf galaxies.

We have to explore the Magellanic Corona directly, but the team model provides a toolkit to do so.

The gas cloud must contain highly ionized states of carbon and silicon. Using the Hubble Space Telescope, we can see distant quasars through the Magellanic Corona, and to see if it travels through important clouds of these materials along the way to the solar system, their light. Will analyze

The researchers wrote in their paper, “Background-Kaiser visualizations provide a chance for obscure spies of the Magellanic corona, as they are uncontrolled by the interstellar material of the large Magellanic cloud.”

The research has been published in Nature.

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